Since antibodies have high binding activity, binding specificity and high stability in blood, their applications to the diagnosis, prevention and treatment of various human diseases have been attempted (Monoclonal Antibodies: Principles and Applications, Wiley-Liss, Inc., Chapter 2.1 (1995)). However, an antibody derived from an animal other than human, such as a mouse antibody, is recognized as a foreign material when administered to a human, which thereby induces a human antibody against the mouse antibody (human anti-mouse antibody: hereinafter referred to as “HAMA”) in the human body, and it is known that the HAMA causes side effects by reaction with the administered mouse antibody (J. Clin. Oncol., 2, 881 (1984); Blood, 65, 1349 (1985); J. Natl. Cancer Inst., 80, 932 (1988); Proc. Natl. Acad. Sci. U.S.A., 82, 1242 (1985)), promotes disappearance of the administered mouse antibody from blood (J. Nuc. Med., 26, 1011 (1985); Blood, 65, 1349 (1985); J. Natl. Cancer Inst., 80, 937 (1988)) and reduces diagnostic, preventive and therapeutic effects of the mouse antibody (J. Immunol., 135, 1530 (1985); Cancer Res., 46, 6489 (1986)).
For the purpose of solving these problems, attempts have been made to convert an antibody derived from an animal other than human into a humanized antibody, such as a human chimeric antibody or a human complementarity determining region (hereinafter referred to as “CDR”) a grafted antibody, using gene recombination techniques. The human chimeric antibody is an antibody in which its antibody variable region (hereinafter referred to as “V region”) is of an antibody of an animal other than human and its constant region (hereinafter referred to as “C region”) is of a human antibody (Proc. Natl. Acad. Sci. U.S.A., 81, 6851 (1984)). It has been reported that administration of such chimeric antibodies to humans eliminate serious side effects and the half-life in blood was prolonged about 6 times compared to a mouse antibody (Proc. Natl. Acad. Sci. U.S.A., 86, 4220 (1989)). The human CDR-grafted antibody is an antibody in which CDR of a human antibody is replaced by CDR of an antibody other than human (Nature, 321, 522 (1986)). It has been reported that, in an experimentation using monkey, the immunogenicity of a human CDR-grafted antibody was reduced and its half-life in blood was prolonged 4 to 5 times compared to a mouse antibody (J. Immunol., 147, 1352 (1991)). These reports show that a humanized antibody is expected to have sufficient effects, as an antibody to be applied to the diagnosis, prevention and treatment of various human diseases, even though it is not a completely human antibody. Actually, clinical tests have been performed with anti-tumor antibodies, such as an anti-CD2O human chimeric antibody, Rituxan (IDEC, Inc.), and an anti-HER2/neu human CDR-grafted antibody, Herceptin (Genentech, Inc.). The safety and therapeutic effects of the anti-CD20 human chimeric antibody and of the anti-HER2/neu human CDR-grafted antibody, to a certain degree, have been confirmed in B lymphoma and breast cancer, respectively (J. Clin. Oncol., 16, 2825 (1998); J. National Cancer Institute, 90, 882 (1998)). Moreover, a fragment (Fab′) of an anti-GPIIb/IIIa human chimeric antibody, ReoPro (Centocor, Inc.), is commercially available in Europe and America as a secondary disease preventing drug after percutaneous transluminal coronary angioplasty. Currently, a large number of clinical tests are being conducted with other humanized antibodies. Most of these humanized antibodies have been prepared using gene recombination techniques and produced using appropriate animal cells.
It has been revealed that five classes of antibodies, i.e., IgM, IgD, IgG, IgA and IgE, are present in mammals. Antibodies of human IgG class are mainly used in the diagnosis, prevention and treatment of various human diseases because of their long half-life in blood and functional characteristics, such as various effector functions and the like (Monoclonal Antibodies: Principles and Applications, Wiley-Liss, Inc., Chapter 2.1 (1995)). The human IgG class antibody is further classified into the following 4 subclasses: IgG1, IgG2, IgG3 and IgG4. A large number of studies have so far been carried out for the antibody-dependent cellular cytotoxicity activity (hereinafter referred to as “ADCC activity”) and complement-dependent cytotoxicity activity (hereinafter referred to as “CDC”) as effector functions of the IgG class antibody, and it has been reported that antibodies of the IgG1 subclass have the greatest ADCC activity and CDC activity among the human IgG class antibodies (Chemical Immunology, 65, 88 (1997)). Therefore, most of the anti-tumor humanized antibodies which require a high effector function are antibodies of human IgG1 subclass, including the above Rituxan and Herceptin.
Expression of ADCC activity and CDC activity of human IgG1 subclass antibodies requires binding of the Fc region of antibody to an antibody receptor existing on the surface of an effector cell, such as a killer cell, a natural killer cell, an activated macrophage or the like (hereinafter referred to as “FcγR”) and various complement components. It has been suggested that several amino acid residues in the second domain of the antibody hinge region and C region (hereinafter referred to as “Cγ2 domain”) (Eur. J. Immunol., 23, 1098 (1993), Immunology, 86, 319 (1995), Chemical Immunology, 55, 88 (1997)) and a sugar chain linked to the Cγ2 domain are also important for this binding reaction (Chemical Immunology, 65, 88 (1997)). Regarding the sugar chain, Boyd et al. have examined effects of a sugar chain on the ADCC activity and CDC activity, by treating a human CDR-grafted antibody, CAMPATH-1H (human IgG1 subclass), produced using Chinese hamster ovary cell (CHO cell) or mouse myeloma NS0 cell with various sugar hydrolyzing enzymes, and reported that elimination of sialic acid of the non-reducing terminal does not have influence upon both activities. Further elimination of galactose residue however was reported to exert influence upon only the CDC activity, decreasing about 50% of its activity. Complete elimination of the sugar, chain was reported to cause disappearance of both activities (Molecular Immunol., 32, 1311 (1995)). Moreover, Lifely et al. have analyzed the sugar chain of a human CDR-grafted antibody, CAMPATH-1H (human IgG1 subclass) which was produced using CHO cell, NS0 cell or rat myeloma YO cell, measured its ADCC activity and reported that the CAMPATH-1H derived from YO cell shows the greatest ADCC activity, suggesting that N-acetylglucosamine at the bisecting position is important for the activity (Glycobiology, 5, 813 (1995): WO 99/54342). These reports show that the structure of sugar chain plays an important role in the effector function of human IgG1 subclass antibodies, and that it may be possible to prepare an antibody having greater effector function by changing the sugar chain structure. Actually, however, structures of sugar chains are complex and vary greatly. There exists a need therefore to further study the structure in order to obtain greater effector function.